Adding REST API to show all availability zones of an region

Returns a summary or detailed list of availability zone to client.
To keep consistent result with EC2 API and de-duplicate, I have
refactored EC2 cloud controllor code.

Implement one workitem for bp:show-availability-zone

Change-Id: I6c9c673c757c6c319a1cdd94d7420b8983f92bbb
Signed-off-by: zhiyanliu <zhiyanl@cn.ibm.com>
Merge "Adding REST API to show all availability zones of an region"